使用view.bounds来创建边界

Answer 1

你肯定想要使用它的超视图的界限来约束它的运动。

不要经常调用setNeedsDisplay。在方法结束时调用一次。你可能不必要地重绘。

我会使用以下内容来完成此任务。

// define these variables where ever you'd like
static float maxX = 0.;
static float maxY = 0.;
static float minX = 0.;
static float minY = 0.;

- (void)setupView {
    CGRect b = [self bounds];

    // calculate constraints
    maxX = b.origin.x + b.size.width/* - [box bounds].size.width */;
    minX = b.origin.x;
    maxY = b.origin.y + b.size.height/* - [box bounds].size.height */;
    minY = b.origin.y;
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    startLocation = [touch locationInView:self];

    // apply constraints
    touchLocation.x = MIN(maxX, startLocation.x);
    touchLocation.x = MAX(minX, startLocation.x);
    touchLocation.y = MIN(maxY, startLocation.y);
    touchLocation.y = MAX(minY, startLocation.y);

    [self setNeedsDisplay];
}